The present invention relates to a device, of the resistive matching quadrupole type, for matching, a reactance of the resistance/inductance/capacitance type (in series or in parallel), and providing a standing wave ratio equal to zero or very low in all cases, irrespective of the input frequency, within a very wide range of frequencies. The invention is more particularly applicable to microwaves (hyperfrequencies) and the reactance matched advantageously consists of a transistor or of a microwave amplifier.
In the microwave range, the utilization of bipolar transistors or of field effect transistors of gallium arsenide or elements of groups III-V, is ever more widespread, for several reasons:
simplicity of application, PA1 low supply voltages, PA1 high gains, PA1 very high cut off frequency. PA1 feedback amplifiers, PA1 resistive matching amplifiers, PA1 distributed amplifiers. PA1 compensates for the loss of gain of a transistor or of an amplifier as the frequency rises, PA1 provides a SWR value at the input and/or output, which is approximately equal to one, to the extent that the equivalent layout of the matched transistor is known, and this in a manner unaffected by the frequency, within a wide range of frequencies. PA1 either the impedance circuit Z.sub.3 situated between the first input and output terminals if the device to be matched is of the RLC in parallel type, PA1 or the impedance circuit Z.sub.4 situated between the junction point between the circuits Z.sub.1 and Z.sub.2 and the point common to the second input and output terminals, if the device to be matched is of the RLC in series type. PA1 first and second circuits in series, having the impedance Z.sub.1 and Z.sub.2 respectively, and a third circuit having the impedance Z.sub.3 in parallel with the two aforesaid circuits, connected between a first input terminal and a first output terminal, PA1 a fourth circuit of impedance Z.sub.4 connected between the point common to the first two circuits and the point common to the second input terminal and the second output terminal, at least one of the third or fourth impedances being that of the reactance which is to be matched, the values of these four impedances being related in such a manner that the quadrupole offers at its input and output terminals, a pure impedance (resistance) and a reactance equal to zero independently of the operating frequency.
Furthermore, the design of microwave amplifiers of the very wide band transistor type, offers considerable interest, especially for satellite communications equipment, instrumentation, countermeasure and other equipment.
Producing an amplifier having a uniform gain throughout a wide band, makes it necessary however to compensate for the loss of gain of the transistors as the frequency rises.
For comparatively small bandwidths, of the order of an octave or less, the design of an amplifier of this nature is based on the techniques for production of loss-free filters, for calculation of the impedance matchers at the input and output of the amplifier, these matches may, like the transistors or amplifiers, be likened to quadrupoles. Arranging several amplifier stages in cascade with such matching quadrupoles is very difficult because the input and output standing wave ratios (SWR) may be very large, especially at low frequency, within the frequency band. As a matter of fact, if the gain of a transistor is attenuated at low frequencies in order to secure a uniform gain, the reflected wave resulting therefrom modifies the input impedance of the transistor.
On the other hand, the utilization of amplifiers of the "balanced" type assures availability of an amplifier well adapted as regards SWR over a wide range of frequencies. In this case, two identical amplifiers are situated between so-called "90.degree. 3 dB" hybrid couplers. The power reflected at the input and output of each of the two individual amplifiers is absorbed by the load applied to the isolated output of the 90.degree. coupler. Low SWR values are consequently assured, and the amplifiers may be connected in cascade.
The greatest limitation for a "balanced" amplifier derives primarily from the coupler. In the present state of technology, the amplification band of a balanced stage is limited to about 2 octaves. Furthermore, a balanced stage requires twice the D.C. biasing power as compared to a single matched stage, since there are two amplifiers in parallel.
Three layouts may be utilized to obtain wide band amplifiers with single matched stages:
However, the input/output SWR values are not very satisfactory in these three cases, acting against connecting several stages in cascade. In the case of the resistive matching amplifier, it becomes even necessary to calculate all the combined stages.